Steel Shear Walls for Existing Buildings

After the 1971 San Fernando earthquake in which two Veterans Administration hospitals collapsed, killing 46 people, the VA initiated an extensive program for evaluating and, if necessary, strengthening all VA hospital buildings in earthquake-troubled areas. One of the facilities that required strengthening was the VA Medical Center in Charleston, South Carolina. Because of the complexity of the project, URS/John A. Blume & Associates, Engineers, San Francisco, was selected to serve as structural consultant to Lafaye Associates, Architects, Columbia, South Carolina. Built in 1963, the center is a complex made up of several buildings having from one to five stories. The three main buildings are separated from one another by 2-in. expansion joints. The total floor area of the five-story complex is 350,000 sq ft. Each building uses reinforced concrete flat slab construction with columns at 20 ft on center each way. The structures were originally designed to resist lateral loads caused by wind only. The lateral forces were carried by isolated stair walls and frame action. Whereas the design base shear caused by wind forces was approximately 3% of the total dead load, the new VA earthquake code requires the strengthened structure to handle a base shear of 15%. The existing reinforced columns would be severely overstressed with a base shear of 15%; thus, the building had to be strengthened.